EP3381039A1 - Degrader comprising boron carbide - Google Patents

Degrader comprising boron carbide

Info

Publication number
EP3381039A1
EP3381039A1 EP16797833.7A EP16797833A EP3381039A1 EP 3381039 A1 EP3381039 A1 EP 3381039A1 EP 16797833 A EP16797833 A EP 16797833A EP 3381039 A1 EP3381039 A1 EP 3381039A1
Authority
EP
European Patent Office
Prior art keywords
degrader
degrading
graphite
active material
energy
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP16797833.7A
Other languages
German (de)
French (fr)
Inventor
Alexander Gerbershagen
Jacobus Maarten Schippers
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Scherrer Paul Institut
Original Assignee
Scherrer Paul Institut
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scherrer Paul Institut filed Critical Scherrer Paul Institut
Publication of EP3381039A1 publication Critical patent/EP3381039A1/en
Pending legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/10—Scattering devices; Absorbing devices; Ionising radiation filters
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
    • A61N5/1043—Scanning the radiation beam, e.g. spot scanning or raster scanning
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1077—Beam delivery systems
    • A61N5/1081—Rotating beam systems with a specific mechanical construction, e.g. gantries
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K5/00—Irradiation devices
    • G21K5/04—Irradiation devices with beam-forming means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N2005/1085—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy characterised by the type of particles applied to the patient
    • A61N2005/1087—Ions; Protons
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N2005/1092—Details
    • A61N2005/1095—Elements inserted into the radiation path within the system, e.g. filters or wedges

Definitions

  • Degrader comprising boron carbide
  • the present invention relates to a degrader, preferably used in particle radiation therapy facilities.
  • a degrader is an amount of material (a block or several layers) with a low atomic number (Z), such as graphite.
  • Z atomic number
  • the degrader, or a part of it, is inserted in the trajectory of the particle beam in order to reduce the energy of the particles.
  • the total thickness of the amount of this material determines the energy of the out-going particles.
  • the particles crossing such material are also scattered by the nuclei in the material.
  • the out-going beam obtains an increase in diameter as well as an increase in angular spread (divergence) .
  • a set of collimators is mounted immediately behind the degrader. When degrading to low energies the scattering increases. At these collimators the losses thus increase, which yields a decrease of the transmission, which is the fraction of the beam intensity from the accelerator, that reaches the patient. In proton therapy this causes an undesirable increase of treatment time.
  • the proton therapy facility PROSCAN consists of a 250 MeV
  • the energy required for the patient treatment is in the range between 70 MeV and 230 MeV.
  • Energy modulation is performed via a graphite degrader ( Figure 2), that is inserted into the beam trajectory, reducing the beam energy from 250 MeV to a value specified by the treatment planning.
  • the intensity loss can be
  • the maximum beam current provided by the cyclotron is, however, limited. Hence, it is useful to examine the possibilities of reducing the emittance increase in the degrader that leads to the beam loss in the subsequent beam transport system.
  • degrader material is graphite, so a material with a low atomic number Z, to limit the multiple scattering amplitude.
  • Beryllium is also a degrader material with a low Z, thus also causing a low divergence increase and it has been used as degrader material at some places. However, it has a
  • a degrader comprising degrading active material wherein the degrading active material comprises Boron Carbide B4C.
  • This degrader evokes an amount of multiple scattering that is lower than in graphite for the same energy loss.
  • B4C increases the transmission by at least 35% for the beam degradation to low energies, which is a significant and useful amount of beam intensity increase in particle therapy.
  • the B4C-material does not become more radioactive than graphite, so that there will be no additional problems at service activities. Further, B4C as degrading active material does not have any toxic properties.
  • the degrading active material can be assembled as plates or as wedges.
  • the degrading active material can be mounted on one or more actuators that can bring the degrader or a part of the degrader in a position where it is crossed by the particle beam.
  • Preferred embodiments of the present invention are hereinafter described in more detail with reference to the attached drawings which depict in: Figure 1 Transmission of a proton current through a degrader, emittance collimators and energy selection section for a beam with an initial energy of 250 MeV, as measured at PSI; Figure 2 a depiction of degrader wedges in the beam trajectory as currently in use at PSI; and
  • B4C is a material of lower average atomic weight and higher density than graphite. Calculations predict that, compared with graphite, the use of B4C results in a lower emittance behind the degrader. Downstream of the acceptance defining collimation system at the entrance of the following beam lines, a higher beam transmission occurs, especially at low beam energies. This is of great interest in particle therapy
  • the results of experiments carried out at the PROSCAN facility at the Paul Scherrer Institute are discussed hereinafter.
  • the simulations of a B4C -degrader have predicted an increase in the beam transmission of approx. 31% compared to graphite, for beam degradation from 250 to 84 MeV .
  • the experiment carried out with a B 4 C block reducing the energy to 84 MeV yielded a transmission improvement of 37% compared with the carbon degrader set to that energy .
  • a B4C block has been used, having a length of 150 mm and transverse dimensions 24 mm x 24 mm, mounted in an aluminum frame with open ends at beam entrance and exit.
  • Fig. 2 shows the graphite degrader 2 having wedges 4 which can be driven into or out of the particle beam 6 in a direction
  • B 4 C degrader might have a similar form in order to be capable of changing the beam energy dynamically.
  • this is not the only layout: there are other options possible, e.g. with only one long wedge and/or rotational wheel or something else.
  • the beam current has been measured after the cyclotron and after the energy selection system for both the B 4 C block and the graphite wedge degrader for a beam energy of 84 MeV.

Landscapes

  • Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Biomedical Technology (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Radiology & Medical Imaging (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Pathology (AREA)
  • Radiation-Therapy Devices (AREA)

Abstract

It is the objective of the present invention to provide a degrader that has excellent degrading capabilities with, for the same energy loss in the degrader, a lower emittance increase as currently used materials, without generating a strong neutron flux and without having severe toxic characteristics. This objective is achieved according to the present invention by a degrader (2) for use in the field of the application of a particle beam (6), comprising degrading active material wherein the degrading active material comprises Boron Carbide B4C. This degrader has an amount of multiple scattering that is lower than in graphite for the same energy loss. The use of B4C increases the transmission by at typically 35% for the beam degradation to low energies, which is a significant and useful amount of beam intensity increase in particle therapy. The B4C-material does not become more radio-active than graphite, so that there will be no additional problems at service activities. Further, B4C as degrading active material does not have severe toxic properties.

Description

Degrader comprising boron carbide
The present invention relates to a degrader, preferably used in particle radiation therapy facilities.
When slowing down (="degrading") protons or ions (particles) from a particle accelerator, such as for example a cyclotron, to an energy compatible with the range of the particles in tissue, this is done by sending the beam through a degrader. A degrader is an amount of material (a block or several layers) with a low atomic number (Z), such as graphite. The degrader, or a part of it, is inserted in the trajectory of the particle beam in order to reduce the energy of the particles. The total thickness of the amount of this material determines the energy of the out-going particles. However, the particles crossing such material are also scattered by the nuclei in the material. Due to this so-called multiple scattering process the out-going beam obtains an increase in diameter as well as an increase in angular spread (divergence) . In order to prevent unwanted beam losses in the beam transport system following the degrader, usually a set of collimators is mounted immediately behind the degrader. When degrading to low energies the scattering increases. At these collimators the losses thus increase, which yields a decrease of the transmission, which is the fraction of the beam intensity from the accelerator, that reaches the patient. In proton therapy this causes an undesirable increase of treatment time.
At Paul Scherrer Institute (PSI) , CH-5232 Villigen PSI, the proton therapy facility PROSCAN consists of a 250 MeV
superconducting cyclotron COMET and a beam transport system that guide the beam to four treatment areas, Gantry 1, Gantry 2, Gantry 3 and OPTIS. The energy required for the patient treatment is in the range between 70 MeV and 230 MeV. Energy modulation is performed via a graphite degrader (Figure 2), that is inserted into the beam trajectory, reducing the beam energy from 250 MeV to a value specified by the treatment planning.
Low energies are used in the treatments in the gantries for dose deposition in the (parts of the) tumors that are located at a shallow position below the skin. The lowest beam energy of 70 MeV requires the maximum energy degradation in PROSCAN and beam transmission is most challenging (see transmission curve in
Figure 1) . This energy is also used for treatments of eye
melanoma at OPTIS. Active participation of the patients is required for eye treatments . The irradiation time should
therefore be as short as possible and, hence, a reasonably high beam intensity is important at the patient. Unfortunately, the multiple scattering process in an energy degrader increases the beam size, divergence and energy spread beyond the beamline and gantry acceptance. It is unavoidable to use one or more collimator systems and an energy selection system to cut these quantities to those that fit in the acceptance of the following beam transport system, to prevent unwanted beam losses in the beam transport system. This limited acceptance depends on the energy, the geometrical layout of the beam
transport system and on the setting of the magnets in this system. At PSI a typical beam transmission is on the order of 0.2% for beams with an energy of 70 MeV.
Typically, for lower energies the intensity loss can be
compensated by an increase of beam current at the cyclotron exit. The maximum beam current provided by the cyclotron is, however, limited. Hence, it is useful to examine the possibilities of reducing the emittance increase in the degrader that leads to the beam loss in the subsequent beam transport system.
The usual choice for degrader material is graphite, so a material with a low atomic number Z, to limit the multiple scattering amplitude. Beryllium is also a degrader material with a low Z, thus also causing a low divergence increase and it has been used as degrader material at some places. However, it has a
disadvantage of creating a strong neutron flux during the degrading of high energy protons. Furthermore, Beryllium is known to have some toxic characteristics. Plastics are also used, but these suffer from geometry changes due to the radiation damage and heat deposition in the material. It is therefore the objective of the present invention to provide a degrader that has excellent degrading capabilities without generating neutron flux and not having toxic properties.
This objective is achieved according to the present invention by a degrader comprising degrading active material wherein the degrading active material comprises Boron Carbide B4C.
This degrader evokes an amount of multiple scattering that is lower than in graphite for the same energy loss. At PSI it has been found that the use of B4C increases the transmission by at least 35% for the beam degradation to low energies, which is a significant and useful amount of beam intensity increase in particle therapy. The B4C-material does not become more radioactive than graphite, so that there will be no additional problems at service activities. Further, B4C as degrading active material does not have any toxic properties.
Suitably, the degrading active material can be assembled as plates or as wedges.
Suitably, the degrading active material can be mounted on one or more actuators that can bring the degrader or a part of the degrader in a position where it is crossed by the particle beam. Preferred embodiments of the present invention are hereinafter described in more detail with reference to the attached drawings which depict in: Figure 1 Transmission of a proton current through a degrader, emittance collimators and energy selection section for a beam with an initial energy of 250 MeV, as measured at PSI; Figure 2 a depiction of degrader wedges in the beam trajectory as currently in use at PSI; and
Test measurements using boron carbide (B4C) as degrader material are discussed in the following in comparison with the
conventional graphite, which is currently used in many proton therapy degraders. B4C is a material of lower average atomic weight and higher density than graphite. Calculations predict that, compared with graphite, the use of B4C results in a lower emittance behind the degrader. Downstream of the acceptance defining collimation system at the entrance of the following beam lines, a higher beam transmission occurs, especially at low beam energies. This is of great interest in particle therapy
applications as it allows either a reduction of the beam
intensity extracted from the cyclotron or a reduction of the treatment time.
The results of experiments carried out at the PROSCAN facility at the Paul Scherrer Institute are discussed hereinafter. The simulations of a B4C -degrader have predicted an increase in the beam transmission of approx. 31% compared to graphite, for beam degradation from 250 to 84 MeV . The experiment carried out with a B4C block reducing the energy to 84 MeV yielded a transmission improvement of 37% compared with the carbon degrader set to that energy . In the experiment a B4C block has been used, having a length of 150 mm and transverse dimensions 24 mm x 24 mm, mounted in an aluminum frame with open ends at beam entrance and exit. The block has been installed in the degrader box at the position of the carbon wedges and aligned in order to provide the same position at the beam exit. The conditions of the transmission measurement with the B4C degrader were similar to those with the graphite degrader. Fig. 2 shows the graphite degrader 2 having wedges 4 which can be driven into or out of the particle beam 6 in a direction
perpendicular to the direction of the particle beam 6. Other B4C degrader might have a similar form in order to be capable of changing the beam energy dynamically. However, this is not the only layout: there are other options possible, e.g. with only one long wedge and/or rotational wheel or something else.
The beam current has been measured after the cyclotron and after the energy selection system for both the B4C block and the graphite wedge degrader for a beam energy of 84 MeV. The
transmission, defined as the ratio of these beam currents, was 0.59 % for the B4C block and 0.43 % for the graphite degrader. Hence, it was found that the measured transmission is 37.2% higher for the B4C block compared to the graphite degrader for the same energy.
Measurements have successfully been performed to compare the experimental behavior with the calculated performance of B4C as potential degrader material. Both simulation and measurement yield an improvement of the transmission at 84 MeV in the order of 35% using a B4C degrader compared to the currently used graphite degrader. Further a 30 % lower dose rate at the B4C degrader is expected compared with the graphite degrader. Thus, the level of B4C activity after the irradiation is considered as acceptable and uncritical with respect to machine maintenance.

Claims

Patent Claims
1. A degrader (2) for use in the field of the application of a particle beam (6), comprising degrading active material wherein the degrading active material comprises Boron Carbide (B4C) .
2. The degrader according to claim 1 wherein the degrading active material is mounted on one or more actuators that can bring the degrader or a part of the degrader in a position where it is crossed by the particle beam.
3. The degrader (2) according to claim 1 wherein the degrading active material is assembled as one element (block) or comprises a number of elements, such as wedges (4) and/or plates.
EP16797833.7A 2015-11-27 2016-11-14 Degrader comprising boron carbide Pending EP3381039A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP15196840.1A EP3174069A1 (en) 2015-11-27 2015-11-27 Degrader comprising boron carbide
PCT/EP2016/077563 WO2017089158A1 (en) 2015-11-27 2016-11-14 Degrader comprising boron carbide

Publications (1)

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EP3381039A1 true EP3381039A1 (en) 2018-10-03

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EP16797833.7A Pending EP3381039A1 (en) 2015-11-27 2016-11-14 Degrader comprising boron carbide

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US (1) US20180277277A1 (en)
EP (2) EP3174069A1 (en)
JP (1) JP2019502906A (en)
KR (1) KR20180086229A (en)
WO (1) WO2017089158A1 (en)

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CN107737411B (en) * 2017-10-13 2018-11-02 华中科技大学 A kind of more wedge-shaped mixing material degraders of varied angle
CN107863173B (en) * 2017-11-01 2019-05-31 中国科学院合肥物质科学研究院 High energy particle degrader part and preparation method thereof
TW202039026A (en) * 2019-03-08 2020-11-01 美商美威高能離子醫療系統公司 Delivery of radiation by column and generating a treatment plan therefor

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DE19907098A1 (en) * 1999-02-19 2000-08-24 Schwerionenforsch Gmbh Ion beam scanning system for radiation therapy e.g. for tumor treatment, uses energy absorption device displaced transverse to ion beam path via linear motor for altering penetration depth
GB2384675B (en) * 2002-01-28 2006-01-11 James Macdonald Farley Francis Energy degrader for particle beams
DE102009058294A1 (en) * 2009-12-05 2011-06-09 Gsi Helmholtzzentrum Für Schwerionenforschung Gmbh Irradiation method and apparatus for carrying out the method
EP2703045B1 (en) * 2011-04-25 2015-11-25 Mitsubishi Electric Corporation Particle beam energy converter, particle beam treatment device provided with same, and particle beam energy converting method
JP5726644B2 (en) * 2011-06-06 2015-06-03 住友重機械工業株式会社 Energy degrader and charged particle beam irradiation system including the same
DE102015106246A1 (en) * 2015-04-23 2016-10-27 Cryoelectra Gmbh Beam guiding system, particle beam therapy system and method

Also Published As

Publication number Publication date
KR20180086229A (en) 2018-07-30
JP2019502906A (en) 2019-01-31
US20180277277A1 (en) 2018-09-27
WO2017089158A1 (en) 2017-06-01
EP3174069A1 (en) 2017-05-31

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